Acrylic fiber bundles are widely used as carbon-fiber precursors. When producing carbon-fiber-precursor acrylic fiber bundles, methods are generally known such as drawing carbon-fiber-precursor acrylic fiber bundles while continuously moving the bundles in one direction using a steam drawing apparatus.
By steam drawing carbon-fiber-precursor acrylic fiber bundles, a high draw ratio is achieved with less fuzz and end breakage, and productivity is enhanced.
Also, as for generally known methods for producing a carbon-fiber-precursor acrylic fiber bundle to obtain high-resistance carbon fibers, oil agents are applied to the fiber during an upper-stream production process using a steam-drawing apparatus and then the fiber is dried for fiber densification.
However, in a drying densification step, it is thought that oil agents cause pseudo-bonding among single yarns of a carbon-fiber-precursor acrylic fiber bundle, thus uniform penetration of steam into the fiber bundle is blocked and the plasticizing effects of the steam are not achieved uniformly in the fiber bundle. Accordingly, it is thought that uniform drawing performance by a steam-drawing apparatus is lowered, causing fuzz and breakage of the fiber bundle. To avoid such pseudo-bonding, for example, Japanese Laid-Open Patent Publication No. H11-286845 (patent publication 1) discloses a method for conducting opening treatment on acrylic filament yarn using a fluid before introducing the yarn into a steam box.
In addition, as described in Japanese Laid-Open Patent Publication No. H07-70862 (patent publication 2), prior to steam-drawing a carbon-fiber-precursor acrylic fiber bundle in a pressurized steam-drawing room, the fiber bundle is squeezed by a yarn squeezing device shortly before being introduced into a steam box. Accordingly, stable draw results are achieved.